The present invention is directed to the pyrolysis of solid organic wastes from industrial and municipal sources and to obtaining a chlorine free pyrolytic oil therefrom.
The disposal of wastes both from municipal and industrial sources, such as trash, rubbish, garbage, animal wastes, agricultural wastes, and waste of plastic processing operations is rapidly becoming of immense national concern. The cost of disposal ranks third behind public schooling and highways as municipal expense in the United States.
It is estimated that each individual in the country generates between 3 and 6 pounds of waste per day, and that the industrial output is equivalent to approximately 5 pounds of solid waste per person per day. Previous methods of mass waste disposal, such as landfill are becoming impossible, while others such as incineration are costly and result in air pollution problems.
A vast majority of the waste which is presently disposed of contains products which are immediately recyclable back into the economy or materials which can be converted into products for recycle back to the economy. Directly recyclable constituents are the various metals present, such as aluminum and steel, and glass. For the most part the organic fraction of the waste is subject to pyrolysis following gross recovery of the directly recyclable inorganic fraction. Pyrolysis yields char, pyrolytic oils and gases as products. Pyrolysis in its broadest definition is heating of the organics when in a comminuted state under essentially non-oxidizing conditions to a temperature at which at least devolatilization of the organics occurs. Generally, although no precise transition exists, pyrolysis products will be predominantly liquids at temperatures below about 1200.degree. F. and by gases at temperature above about 1200.degree. F. In solid waste treating operations, the waste material feed to undergo pyrolysis is an essentially solid carbonaceous material consisting of organics and fly ash and particulate inorganics which escape recovery.
A particularly attractive method for converting the solid organic wastes into new and useful products consists of a process where the waste material is first dried and comminuted to a particle size wherein the largest particle has a maximum particle dimension of less than about 1 inch. There is then formed a turbulent gas stream by admixing the dried comminuted waste material with solid heat source and a carrier gas which does not deleteriously react with or oxidize the organic waste materials or products derived therefrom. The mixture is passed through a transport pyrolysis zone where at a temperature between 600.degree. and 2000.degree. F. the organic wastes undergo pyrolysis yielding solid char and vaporized hydrocarbonaceous constituents. The vaporized hydrocarbonaceous constituent is separable into a pyrolytic oil and a normally gaseous hydrocarbonaceous constituent. The gaseous constituent may be recycled to the process and combusted for heat. A portion of the char is also recycled as the heat source or converted by decarbonization into an inert heat source.
The pyrolytic oils formed, while varying in nature depending upon the composition of the waste material processed and pyrolysis conditions employed, are at the same time unique. They may be characterized as an oxygenated, complex organic fluid, typically up to 40% and in some cases up to 85% soluble in water, acids or base. Solubility in polar organic solvents such as glycerol is limited and the pyrolytic oils are relatively insoluble in non-polar organic solvents, such as diesel oil, carbon tetrachloride, pentane, decane, benzene, toluene and hexane. The pyrolytic oil, however, can be successively blended and mixed with various #6 fuel oils. Combustion stability of the mixture is about the same as that of #6 fuel oil.
A typical example of an elemental analysis of the pyrolytic oil is that obtained from the pyrolysis of a waste material containing about 70% cellulosics. The oil thus obtained will contain from about 52 to about 60% carbon, from about 6 to about 8% hydrogen, from about 1 to about 2% nitrogen and from about 29 to about 33% oxygen. The empirical formula which best fits the pyrolytic oil analysis is C.sub.5 H.sub.8 O.sub.2. Specific gravities range from about 1.1 to about 1.4.
Municipal and industrial wastes can contain various quantities of chlorine. Chlorine sources range from plastics such as polyvinyl chloride to animal feed lot wastes. One municipality has estimated that the chlorine content of trash will range from 0.7 to about 1.8% by weight, with a mean estimate of 1.3%. Considering a 500 ton per day plant processing municipal waste, the potential hydrogen chloride output from the plant amounts to 6.7 tons per day.
Not only is the hydrogen chloride worth recovering as hydrochloric acid, but also presents problems of corrosion and secondary disposal problems from a pollution standpoint which must be coped with.
At the same time, hydrogen chloride should not be recovered as a component of the pyrolytic oil, since one of the principal end uses for the pyrolytic oil is as a fuel oil. Understandably, it would also be desirable to have the vent gases from the combustion of the fuel essentially free of hydrogen chloride from both a corrosion and pollution standpoint.